The present disclosure relates generally to the field of nonvolatile memory devices, and more specifically to a resistive random access memory device (RRAM).
RRAM is an advantageous form of non-volatile memory in that it has a low operating voltage, high-speed characteristics, and good endurance. A memory cell element (also referred to as a memory element) of an RRAM device functions by determining a change in electrical resistance of a film, typically a metal oxide film, the resistance corresponding to the stored information (e.g. a value of “0” or “1”). An RRAM device typically includes an array of such memory cells, however, for convenience a single memory cell will be discussed herein. In particular, a memory cell of the RRAM device includes a data storage element that has two electrodes and a variable resistive material layer interposed between the two electrodes. The variable resistive material layer (also known as the data storage layer, memory thin film, or resistive thin film) has a reversible variation in resistance according to the polarity and/or the magnitude of an electric signal (e.g. voltage or current) applied between the electrodes. The variable resistive material layer is typically formed of transition metal oxide.
When a voltage is applied to the lower and/or upper electrode, a current may flow through the variable resistive material layer. The current does not flow uniformly, but follows a random path based upon crystalline state of the layer. The variation of the resistance produced for a particular applied voltage is of concern. The variation may cause performance issues for the RRAM device including decreased reliability and increased power consumption. This variation of resistance has been improved by processes such as using a plug contact for the bottom electrode. Improvements were also shown by inserting a buffer layer between the electrodes and the resistive material layer. However, these improvements have disadvantages including, for example, requiring additional process steps for the fabrication of a memory cell. Additional process steps may also be required in the fabrication of conventional RRAM in order to fabricate circuitry to limit the on/off current, as the conventional RRAM devices may not be self-limiting.
As such, an improved memory cell for RRAM device and method of fabricating the same is desired.